This proposal outlines a series of experiments designed to test and refine our understanding of the mechanisms by which the developing nervous system is precisely patterned. Such precision is essential to the normal functioning of the brain; the means by which such patterning arises is essential to both our understanding of normal fetal development, and for developing therapies for the recovery from disease and injury-induced trauma to the nervous system. The ability of researchers to experimentally analyze brain development in vertebrates, however, is limited by the complexity of the vertebrate nervous system and difficulties making appropriate experimental manipulations. This proposal therefore outlines an ongoing series of experiments which examine the patterned development of the peripheral nervous system in the wing of the fruitfly, Drosophila melanogaster. In the fruitfly wing, the individual elements of the PNS arise in an extremely stereotyped fashion from a single epithelial sheet. The relative simplicity of the system and the availability of a number of molecular and genetic tools make it very favorable for experimental analyses. We will use a combination of genetic, molecular, and immunohistological techniques to analyze the molecular basis of this stereotypy. Our analysis includes the development of novel techniques, testing the roles of a number of known genes, and initiating a search for novel genes critical to the patterning process. The specific aims of this project are to: l) Further develop methods for the analysis of lethal mutations in the developing wing using marker- carrying chromosomes and the FRT-FLP system, and develop novel methods for inducing the overexpression of chosen genes in discrete portions of the wing; 2) Describe detailed events of Achaete-scute Complex (AS-C), helix- loop-helix (HLH), and neurogenic gene expression during sensillum precursor development in the wing blade, using immunohistological techniques; 3) Test the role of "inhibitory" HLH genes in controlling normal sensillum development by using mosaic analysis and PNS-specific cell markers; 4) Experimentally analyze the nature of the cell-cell interactions responsible for refinement within "proneural" regions of the wing blade, using genetic and surgical techniques; 5) Examine the role of shaggy, a serine-threonine kinase, in establishing positional information in the wing blade, by probing for known and novel genes whose transcription is altered by the shaggy mutation; and 6) Isolate and analyze novel positionally regulated genes, using enhancer trap Drosophila lines.